"There have been some settlements," said Ari Schwartz, deputy director for the Center for Democracy and Technology in Washington, D.C. "But these guys do have money and they can fight. You have to have a pretty strong class-action suit to fight them."

The suit against 180solutions Inc., filed last year in U.S. District Court in Chicago, was dismissed with prejudice, meaning the lawsuit cannot be brought back.

The defendant called the decision a "very big win."

"It was a case without merit," said Ken McGraw, chief compliance officer for 180solutions, a Bellevue, Wash., firm that was renamed Zango in June. "They claimed we were a spyware company and that we trespass on people's computers. We don't do that; we are invited on the customer's computer."

Shawn Collins of The Collins Law Firm, along with Varga Berger Ledsky Hayes & Casey, a Chicago firm, filed the suit on behalf of three plaintiffs.

Collins hoped the suit could be termed a class action, with the potential of collecting damages for thousands of computer users who have unsolicited spyware on their computers.

Collins said Wednesday the dismissal was not a win for Zango.

"I didn't believe that class certification was available through these plaintiffs," he said, without elaborating. "Since it was a class action we were pursuing, it made no sense to keep litigating.

"Zango didn't prove a single thing," Collins added. "We agreed to drop it. There was no court ruling in favor of 180solutions or Zango."

Despite the dismissal with prejudice, Collins will not stop going after companies he believes pollute computers with spyware.

In a case settled in February, Sotelo vs. Direct Revenue, he successfully argued that spyware companies were trespassing on personal property, a tactic lifted from environmental law. As a result, Direct Revenue agreed not to install software on a computer without the user's consent, among other things.

Because spyware companies typically bundle that software with other programs, such as games or a screensaver, users often do not realize they have agreed to download the software. Spyware code can create numerous problems, ranging from incessant pop-up ads to programs that monitor a user's keystrokes, potentially a way for thieves to steal personal information.

Collins has used the trespass argument in several pollution cases since 2000.

Even in a case he lost, he obtained a $2 million settlement for his clients.

While Schwartz admires what Collins is trying to do, he believes fighting spyware companies is best left to law enforcement agencies with more resources and state attorneys general, including New York's Eliot Spitzer.

According to an August report by the Center for Democracy and Technology, some states and federal agencies are starting to apply existing statutes in cases.

The Federal Trade Commission, for instance, has brought six cases to date under its unfair and deceptive practices authority while the Justice Department has pursued spyware cases using the Wiretap Act.

The pressure from these agencies, Schwartz noted, is leading some spyware companies to change their practices.

McGraw said his company does not put spyware on a user's computer. Zango downloads free games and screensavers to a user's computer in exchange for permission to deliver ads while the user surfs the Web.

If you type the words "laptop computer" into a search box for instance, a pop-up from a technology company may appear.

When a user downloads a Zango game, he must agree to a "plain language disclosure . . . that we are going to serve ads based on your Internet search habits," McGraw said. "Our model is keyword based, like Google."

He added that the software is easy to uninstall if a user no longer wants it on his computer. Zango says it signs up 200,000 new users each day.